Lady Gaga’s long-suffering former assistant Jennifer O’Neill, whom the star branded a “f - - king hood rat” during a bruising court battle, is working on a dishy book about the singer called “Fame Monster.”

O’Neill — who worked for Gaga during the “Born This Way” superstar’s 2009-2011 Monster Ball tours and sued in 2011, claiming that she was owed $393,000 for 7,168 hours of overtime, plus damages — has struck a deal with Simon & Schuster imprint Atria Books, Page Six has exclusively learned.

Insiders say the deal could be worth up to $1 million, which more than makes up for all the overtime O’Neill claims she was forced to work for Gaga, including sleeping in her boss’ bed and administering her daily “medicine.”

Paul Olsewski, Atria Books’ vice president and director of publicity, confirmed that they have a book deal with O’Neill, adding that no release date has yet been set for “Fame Monster.”

While O’Neill has not yet delivered her manuscript to Atria, her Manhattan federal court battle with Gaga provided a glimpse of some fascinating potential “monstrous” material.

O’Neill testified she was “required” to sleep in Gaga’s bed “because she didn’t sleep alone,” and was expected “to be working and available 24/7” for an annual salary of $75,000.

I had no privacy, no chance to talk to any family, no chance to talk to any friends, no chance to have sex if I wanted to have sex.

- Jennifer O’Neill during her court battle with Lady Gaga

O’Neill noted, “I had no privacy, no chance to talk to any family, no chance to talk to any friends, no chance to have sex if I wanted to have sex. There was no chance to do anything.”

Gaga fought the suit and blasted her former aide in a sworn deposition as a “f - - king hood rat who is suing me for money that she didn’t earn.”

The star declared in court papers that “I am the queen of the universe, every day,” and “I’m quite wonderful to everybody that works for me.”

In October 2013, Gaga agreed to settle O’Neill’s suit out of court. Terms were not disclosed. O’Neill’s attorney Virginia Trunkes last night declined to comment on whether her client had avoided signing a nondisclosure agreement. A rep for Gaga didn’t get back to us.